The mayor of London has defended the decision to allow Wembley Stadium to host more than 60,000 fans per match in the final stages of the Euro 2020 football tournament.

Sadiq Khan, who was re-elected in May, said he was “confident” that games would be safe because of requirements for spectators to provide proof of vaccination or a negative Covid test.

“What we’ve seen is people behaving themselves . . . the combination of requiring fans to have either had both jabs or the lateral-flow test means we know that people aren’t taking the virus with them to the stadium,” he told the Financial Times.

Angela Merkel, German chancellor, and Italian prime minister Mario Draghi have both raised concerns over holding Euro matches in the UK because of fears over the spread of the Delta variant of coronavirus first identified in India. Horst Seehofer, German interior minister, last week called for fewer fans at Wembley.

Although the stadium will not be at full 90,000-capacity, the matches are among the largest mass gatherings in the UK since the pandemic forced live sports behind closed doors. The British Grand Prix Formula One race will welcome up to 140,000 fans later this month.

The mayor’s plan for London to lead an economic recovery via large sporting and cultural events faces significant hurdles, despite the planned lifting of almost all social restrictions on July 19. Such events will determine whether mass gatherings can take place without triggering a fresh surge in Covid cases.

Excitement is growing among English football fans after a confident 4-0 victory over Ukraine ahead of the match against Denmark on Wednesday.

Khan said he had spoken to the government about how to allow people to “celebrate in a safe way” in the event England win the Euros, which would be the team’s first major tournament victory since the 1966 Fifa World Cup

“It’s really important we try to find [ways of celebrating] because if we don’t, people find ways of celebrating themselves,” he warned. “But let’s not count our chicks yet.”

Although in favour of opening stadiums, Khan is cautious about the Conservative government’s decision to remove the legal requirement to wear masks. He and Labour party leader Keir Starmer both want mask-wearing to remain the norm on public transport.

But Khan was less prescriptive over the use of masks in some enclosed venues, such as performing arts spaces, which have been hit hard by the stringent self-isolation rules.

“In theatres, you’re not cheek by jowl . . . A theatre is very different from a care home or rush-hour public transport,” he said.

Productions in London’s West End including Hairspray and the Joseph and the Amazing Technicolor Dreamcoat were suspended after show members came into contact with people who had tested positive for Covid-19.

Quarantine rules will be eased from August 16 but venues will be wary of reopening on a large scale without insurance for virus-related cancellations. Insurers have withdrawn from the market, leaving producers and investors to shoulder the financial risks of closures that follow changes in social restrictions or infections.

In spite of his hopes that cultural events will underpin a recovery, Khan warned that large productions faced an uncertain threat. “I’m really worried about the viability of some of our productions going forward,” he said.

Khan has joined the theatre industry in urging the government to provide a state-sponsored insurance scheme.

However, Oliver Dowden, culture secretary, last week told MPs that if the commercial market failed to provide cover after July 19, “we will look at whether we can extend insurance with some sort of government-backed scheme and we are engaging extensively with the Treasury and other government departments to see what that might look like.”